1. Field of the Invention
This invention relates to a swash plate compressor.
2. Background Information
In general, a swash plate compressor includes a swash plate which is fitted on a drive shaft, for rotation in unison with the drive shaft, and a plurality of pistons each of which is connected to the swash plate via a pair of generally hemispherical shoes sliding on front and rear sliding surfaces of the swash plate, respectively, for reciprocation within a cylinder bore according to the rotation of the swash plate.
Each of the pistons is comprised of a body formed with a first concave portion for slidably supporting one of the shoes, a front end portion formed with a second concave portion for slidably supporting the other of the shoes, and a bridge integrally formed with the body and the front end portion for connecting the two portions to each other.
The first and second concave portions are opposed to each other axially, i.e., in a direction of reciprocation of the piston with space therebetween.
The pair of shoes are arranged on opposite outer peripheral portions of the swash plate such that they are opposed to each other via the swash plate to form an imaginary sphere.
As the swash plate rotates, each piston reciprocates within a corresponding one of the cylinder bores, whereby refrigerant gas within the cylinder bore is compressed.
In a swash plate compressor for use in a typical refrigeration cycle system using a chlorofluorocarbon as a refrigerant, an imaginary sphere formed by a pair of shoes has a diameter which is approximately half as large as an outer diameter of each piston.
On the other hand, in a swash plate compressor for a transcritical refrigeration cycle system using carbon dioxide (CO2) as a refrigerant, delivery quantity or capacity of the compressor is approximately a sixth of that of the compressor using the chlorofluorocarbon, due to differences in properties between the two refrigerants. Therefore, each piston of the compressor using CO2 has an outer diameter smaller than that of the piston of the compressor using chlorofluorocarbon. More specifically, the former may be less than half of the latter.
However, since the transcritical refrigeration cycle is a high-pressure cycle in which load applied to shoes by compression pressure during each compression stroke is no lower than when the chlorofluorocarbon is compressed, it is required that the imaginary sphere formed by the pair of shoes has a diameter which is substantially equal to or slightly larger than the outer diameter of the piston, in view of rigidity of the shoes and slidability between the shoes and the swash plate.
Therefore, if the conventional construction of the piston (in which the bridge and the front end portion do not extend radially outward with respect to the peripheral surface of the body) is employed, it is inevitably required to reduce the shoes in size, which makes it impossible to obtain the required rigidity and slidability of the shoes.
It is an object of the present invention to provide a swash plate compressor which is capable of employing shoes suitable in size for a load applied to the shoes and a sliding condition of the shoes.
To attain the above object, the present invention provides a swash plate compressor comprising:
a cylinder block having a plurality of cylinder bores axially formed therethrough;
a housing secured to the cylinder block and having a crankcase defined therein;
a drive shaft extending through the crankcase;
a swash plate received within the crankcase and mounted on the drive shaft, for rotation in unison with the drive shaft, the swash plate having sliding surface on one side facing toward the cylinder block and another side remote from the cylinder block, respectively;
a plurality of pairs of shoes each having a substantially semispherical shape, each pair of the shoes sliding on the sliding surfaces of the swash plate on the one side and the another side, respectively;
a plurality of pistons received in the cylinder bores, respectively, the pistons each connected to the swash plate via a corresponding pair of the pairs of shoes and performing a linear reciprocating motion within a corresponding one of the cylinder bores, as the swash plate rotates; and
a plurality of guide grooves each axially formed in an inner peripheral wall of the housing in a manner such that the guide grooves each extend along a path of the linear reciprocating motion of a corresponding one of the pistons,
the pistons each having:
a body having a first concave portion formed therein for supporting one of a corresponding pair of the pairs of shoes,
a swash plate-side end having a second concave portion formed therein for supporting another of the corresponding pair of the pairs of shoes, and
a bridge formed integrally with the body and the swash plate-side end, the bridge integrally connecting the body and the swash plate-side end in a manner such that the first concave portion and the second concave portion are axially opposed to each other with space therebetween,
the bridge extending radially outward with respect to a peripheral surface of the body of the piston, and being slidably fitted in a corresponding one of the guide grooves,
wherein the pistons are made of an aluminum-based material,
wherein the shoes are made of an iron-based material, and
wherein a ratio of an outer diameter of the body to a diameter of an imaginary sphere formed by the corresponding pair of the pairs of shoes is within a range of 8/10 to 9/10.
According to this swash plate compressor, the bridge of each of the piston is formed radially outward with respect to the outer peripheral surface of the body of the piston. Therefore, the first and second concave portions are formed to have a sufficiently large size, allowing each shoe to have a correspondingly large size which ensures required rigidity of the shoe.
Preferably, the swash plate compressor includes a bearing supporting one end of the drive shaft,
the cylinder block having a central portion formed with a bearing-receiving chamber for receiving the bearing therein, and at least one lubricant supply passage for supplying lubricant collected in at least one of the guide grooves to the bearing-receiving chamber.
According to this preferred embodiment, the bridge of the piston reciprocates within the guide groove along the path of the linear reciprocating motion of the piston to thereby supply lubricant from the guide groove to the bearing-receiving chamber via the lubricant supply passage. This ensures lubrication of the bearing within the bearing-receiving chamber, which improves durability of the bearing.
Preferably, the at least one of the guide grooves includes a guide groove formed at a lowermost location of the inner peripheral wall of the housing.
Preferably, the at least one lubricant supply passage opens into a cylinder block-side end of a corresponding one of the guide grooves.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with accompanying drawings.